1. Technical Field
The disclosure relates generally to integrated circuit (IC) chip fabrication, and more particularly, to a wafer holding robot end effecter vertical position determination in an ion implanter system.
2. Background Art
Ion implantation is a standard IC chip fabrication technique for introducing conductivity altering impurities into, or doping, semiconductor wafers. A typical ion implantation process uses an energetic ion beam to introduce impurities into semiconductor wafers. Introducing the impurities at a uniform depth and dose into the wafers is important to ensure that semiconductor devices being formed operate properly.
As part of IC chip fabrication, and in particular, ion implantation, wafers are moved by multi-axis wafer handling robots from front opening unified pods (FOUPs) that carry the wafers between work locations and the particular work stations. In terms of ion implantation, wafer handling robots typically move wafer(s) from the FOUP, through a load locks (environmental buffer) to an implanting station of an ion implanter system. Each wafer handling robot includes a robotic arm to which an end effecter, which holds one or more wafers, is attached. Each end effecter may include a number of blades, each of which holds a wafer. Each blade may be moved independently of the other blades.
Conventionally, vertical movement of the end effecter is attained by use of a rotary motor coupled to a belt that turns a ball screw (worm gear) that is coupled to the end effecter. Operation of the rotary motor turns the ball screw and moves the end effecter vertically. The location of the end effecter is determined based on an encoder in the rotary motor. That is, the vertical position of the end effecter is determined by data from the rotary motor. One challenge, however, is that, over time, the vertical position of the end effecter relative to the rotary motor can vary. For example, the relative positions can vary due to, among others: slip in relative position of the end effecter, the belt and/or the ball screw; stretching of the belt; gear wear; bending of the end effecter. As a result, the encoder may incorrectly report where the end effecter is vertically positioned. When the vertical position determination is inaccurate, the risk of misalignment of the end effecter with openings through which wafers must pass may occur. In this case, the end effecter or wafer(s) may be damaged.